This invention relates to water management, and in particular, to an apparatus for collecting and diverting runoff surface water or waste water and controlling the flow and direction of subsurface water.
The control and flow of surface water, such as rain water, is important in preventing damage to foundations and basement flooding as well as damage to other structures. Unmanaged surface water also causes soil erosion, plant damage and is the primary cause of non-point source pollution damaging 80% of all water resources. Equally important is the ability to conserve surface runoff as well as waste water for reuse.
Soil composition is an important consideration in planning a drainage system. There are three basic types of soil, i.e., sand, silt and clay. Each of these soils have different drainage and retention capacity. Sand granules are larger and more porous which provide good drainage. Silt granules are smaller and more densely packed which slows the drainage process. Clay granules are smooth and tightly packed which tends to retain water.
It is not uncommon to encounter blends of the basic soil types along with various granules of crushed and larger stone gravel. The effects of soil types in an area selected for sub-surface leaching (absorption) are as follows. Sandy, gravely soil is best and will drain away runoff water quickly. Silty soil will absorb water in time. Clay soil can restrict absorption and retain water within the excavation for an extended period of time. Soil composition, therefore, is a controlling factor in the leaching process, i.e., dispersion of unwanted surface water underground.
To install an effective leaching system, there are other factors to consider, in addition to soil composition. An estimate of the volume of water entering the drainage system and the size of a reservoir established to receive the water. A leaching reservoir temporarily holds water allowing time for it to disperse into the surrounding soil. The size of the reservoir required is determined by the surrounding soil. Sandy soil requires a smaller reservoir as the water is dispersed quickly. Clay soil requires a larger reservoir to provide more time for absorption and evaporation.
Generally, leaching reservoirs are drywells employed to receive therein surface water and to permit the discharge of the surface water beneath the ground and away from the foundation, wall or structure and over a defined area. The basic purpose is to prevent flooding, erosion, washout and plant damage to residential landscapes, industrial properties, recreational, e.g., golf courses, properties and farms.
In the past surface water was commonly trenched or piped to a hole in the ground filled with stone, known as a drywell. Typically a drywell would comprise an open pit or a container optionally filled with loose aggregate material, such as gravel or loose stones, into which the surface water is directed either by a grate on the top surface wherein the top surface of the drywell is generally flush or slightly below the ground level or from a pipe which may be connected to the source of surface water, such as rain water from a downspout, and which permits the discharge of the water into the drywell. However, in time voids in the aggregate material fill with silt and debris and the drywell becomes ineffective.
Other prior art drywells have been built with bricks or masonry blocks. The masonry structures were built with open spaces between the sidewall blocks allowing water to seep out into the surrounding soil. These drywells were typically surrounded with stones to prevent backfill soil from entering the sidewall spaces and thus clogging the masonry drywell. However, the voids in the surrounding stone would often become plugged with soil thus limiting or preventing outflow. Another limitation of the use of stone is the cost and labor intensity of larger excavations to accommodate the stone, plus the added cost of hauling and installing stone to prevent intruding backfill soil.
An alternative to surrounding a reservoir with stone is to wrap the exterior drywell sidewall with geotechnical fabric. It was anticipated that such fabric would be long lasting and provide the obvious cost saving benefits when compared to installing stone. Aside from the potential difficulties related to fabric displacement during the backfilling process leaving the drywell sidewall ports exposed, over time geotechnical fabrics deteriorate triggering complete failure of the system. Another major concern with the use of geotechnical fabric is that silt and debris from runoff water often clog the inner side of the fabric. Leaves, twigs and silt collected in eve troughs or traveling along the ground in storm water commonly enter a drywell. Once inside a reservoir wrapped with geotechnical fabric debris becomes trapped against the fabric covering outflow ports impeding the leaching process.
Applicant has previously developed simplified water management solutions with modularized drywells that may be installed in various terrains in limited or open spaces. See U.S. Design Pat. Nos. D576,714; D350,816; D350,815; D350,814; and U.S. Pat. Nos. 5,249,885; 5,195,284; 5,131,196; 5,086,594; 4,983,069; and 4,982,533, all incorporated by reference. Applicant's previously developed drywell units offered a variety of lightweight, low impact installations to mitigate wet basements as well as damage to landscape features. Applicant's basic drywell unit is a single 50 gallon reservoir for small drainage projects. The basic unit is designed with the capability to stack or interconnect with additional units to accommodate larger volumes of water.
Utilizing data resulting from past installations, applicant has continued his efforts to improve the efficacy of the modular design concept. Given that soil conditions are a controlling element in designing water management solutions, it is apparent that reservoir capacity and outflow are the primary mitigating components in subsurface leaching systems.
It had become apparent to applicant, that a single reservoir may be only sufficient for small volumes in good leaching soil. To increase leaching capacity in the prior art, sidewall leaching was added as the reservoir filled due to soil saturation at the drywell bottom. Sidewall leaching is beneficial, however absorption into the surrounding soil is limited. As water exits through drywell sidewall ports, the exiting water tends to flow downward following the reservoir wall. As a result, the majority of the leaching plume is at the base of the reservoir.